The present invention relates to signaling lamps, in particular in the area of traffic signals and traffic signs. From a particular point of view, it relates to signaling lamps for traffic lights.
In general, lamp technology is not only applied in illumination tasks. The area of signaling lamps is also an important field in lamp technology. The term signaling lamp should in this case be understood primarily to be a lamp which provides information to the observer (informs) about an event or a state. This information is generally already imparted to the observer by the on or off state of the lamp. Furthermore, the lamp may impart additional information content to the observer, for example by means of its shape, color or a legend.
Signaling lamps are used in very many areas of daily life, for example in road traffic, in marine transport and in railroads. Furthermore, they play a role in virtually all forms of technical equipment to be operated or monitored by an operator, be it in the area of household appliances or in entertainment electronics. Furthermore, safety signs for buildings or traffic, commercial or industrial installations should be mentioned, for example airports, train stations, cinemas, public buildings and the like. For example, signaling lamps are being used more and more for indicating escape routes, for drawing attention to hazards, and for drawing attention to particular situations for example, a fire alarm and the like.
Typical of the area of signaling lamps are particular requirements on reliability, which are based on the one hand on safety viewpoints and, on the other hand, are necessitated by their widespread uses in terms of numbers and location and the associated considerable effort for servicing and maintenance. Furthermore, in many applications it is necessary or desirable to be able to use particular physical shapes, for example particularly flat signaling lamps.
Conventionally, normal incandescent lamps or incandescent halogen lamps are generally used in signaling lamps. This applies in particular to the numerous signaling lamps which have to be switched on and off during operation.
Incandescent lamps, including incandescent halogen lamps, have significant disadvantages, however: as a result of the use of a more or less fine incandescent filament, they are basically relatively sensitive to vibration, which leads to restrictions in their use, in particular in the traffic sector.
Furthermore, their operating service life is restricted to a few thousand hours, depending on the lamp type and the operating voltage used. However, an early end to this operating service life is very disadvantageous, in exactly the same way as any other type of susceptibility to defects, because of the frequently high numbers and very widespread uses of signaling lamps, as mentioned.
In many applications, the incandescent lamps have to be installed in an optical system, for example one having a reflector and/or with lenses. Such systems are sensitive to misadjustment of a lamp base or other elements. Furthermore, a certain amount of internal soiling, above all in the traffic sector, is basically unavoidable, so that it is generally not possible, even following expensive internal cleaning operations, to reproduce the initial output of the lamp.
Above all in the case of incandescent lamp applications which have an optical system with reflectors or lenses, for example for illuminating a relatively large signaling area or for controlling the radiation direction of the signaling lamps, a relatively cumbersome overall size and shape or a corresponding weight is inevitable, but in many cases is very undesirable.
In addition, LEDs, that is to say light-emitting diodes, are known in the signaling lamp sector. However, they have the disadvantage that the color locus, which is important for signaling lamp applications and often standardized, cannot be adjusted. Occasionally, they are also unsuitable because of the radiation characteristic.
This invention is therefore based on the technical problem of specifying a new signaling lamp having new possibilities for avoiding the abovementioned difficulties. Furthermore, the invention relates to preferred means for producing a signaling lamp according to the invention, to be specific the use of specific phosphors or phosphor mixtures as described below.
According to the invention, provision is made for a signaling lamp as claimed in claim 1 and its uses as claimed in claims 14, 15 and 16. In addition, in claims 3, 4, 10 and 12, the invention specifies phosphors or phosphor mixtures for use in a green, a yellow or a red signaling lamp.
According to the invention, therefore, a fluorescent lamp is provided, in specific terms a fluorescent lamp having a particularly short-wavelength excitation in the VUV range (Vacuum Ultra Violet range), that is to say that a wavelength below 200 nm. Particularly preferred in this case are excitation wavelengths below 185 nm or below 180 nm. Fluorescent lamps have significant advantages over incandescent lamps with regard to their operational service life, reliability and also with regard to the achievable physical shapes and sizes. VUV fluorescent lamps are a technically relatively novel and particularly interesting sector.
This relates primarily to dielectric barrier discharges, above all of noble gases, and primarily also to the dielectric barrier Xe excimer lamp. In relation to the constructional and electrical details of dielectric barrier gas discharge lamps, reference is made to the applications DE-P 43 11 197.1 (WO 94/23442), DE 195 26 211.5 (WO 97/04625), DE 196 36 965.7 and, with regard to the specific applications of a traffic light, primarily to the European parallel application xe2x80x9cFlat signaling lamp with dielectric barrier dischargexe2x80x9d (97122798:8), the respective disclosure content of the abovementioned applications being included by reference in this application. This applies above all to the pulse technique in electrical operation, the electrode configuration for particularly uniformly illuminated lamps and special, primarily flat, overall shapes as well as, as mentioned, the construction of a traffic light from dielectric barrier gas discharge lamps.
In the signaling lamp sector, the colors red, green and yellow have a particular significance, for example in traffic lights, motor-vehicle signaling lamps (yellow and red), marine lamps (green and red for starboard and port) and so on. The invention therefore relates in particular to phosphors and phosphor mixtures with which appropriate signaling lamps can be implemented with VUV excitation. In many cases, standards also have to be complied with, for example in motor-vehicle rear lamps or traffic lights.
To begin with green signaling lamps, according to the invention, the phosphors listed in the claims: BaMgAl10O17:Mn, Zn2SiO4:Mn, Sr4Al14O25:Eu, BaMgAl10O17:Eu, BaCaAl28O45:Eu, LaPO4:Ce,Tb and Y3Al5O12:Ce have been shown to be phosphors which can be used in the VUV excitation range and from which a signal green may be produced by an appropriate mixture. In particular, green signaling lamps can be produced in a particularly simple and thus advantageous way in many applications merely by using the phosphor Sr4Al14O25:Eu. This is because, according to the invention, it has been shown that the corresponding color locus with VUV excitationxe2x80x94see the exemplary embodimentxe2x80x94is located particularly favorably.
Furthermore, it has been shown that signal green tones may be mixed in a flexible manner by using a mixture of BaMgAl10O17:Mn and/or Zn2SiO4:Mn on the one hand, and Sr4Al14O25:Eu and/or BaMgAl10O17:Eu and/or BaCaAl28O45:Eu on the other hand, it being possible to meet appropriate standards, for example for traffic-light green (as shown in the exemplary embodiment for the case of the German DIN Standard).
Additional freedom is obtained by adding a third component of LaPO4:Ce,Tb and/or Y3Al5O12:Ce, which are located at considerably higher x values in the xy color plane. By contrast, the range of lower x values may be obtained by means of the first two abovementioned mixture components of BaMgAl10O17:Mn and Zn2SiO4:Mn at higher y values, and Sr4Al14O25:Eu and, in particular, BaMgAl10O17:Eu and/or BaCaAl28O45:Eu at lower y-values. From among the pairs of phosphors mentioned and/or linked, the following are preferably selected in the sense of the invention:
It has been shown that the phosphor BaMgAl10O17:Eu exhibits relatively poor maintenance, that is to say the maintenance of the yield and of the color locus, over the operating time under VUV irradiation, for which reason Sr4Al14O25:Eu is preferred over it. In addition, Sr4Al14O25:Eu exhibits the position in the xy color chart which is closer to the spectral green point at 550 nm on the spectral curve, which is optimum in terms of the visual effect (that is to say the sensitivity of the human eye).
On the other hand, the maintenance properties of the phosphor BaMgAl10O17:Eu may be improved considerably by means of a hyperstoichiometric proportion of Mg, as described in detail and claimed in the U.S. parallel application xe2x80x9cBarium magnesium aluminate phosphorxe2x80x9d (08/996,926). The disclosure content of this U.S. parallel application is hereby included as well by reference. Overall, however, Sr4Al14O25:Eu is also to be preferred over the BaMgAl10O17:Eu phosphor with a hyperstoichiometric proportion of Mg, above all with regard to the maintenance properties.
In the pairing of BaMgAl10O17:Mn and Zn2SiO4:Mn, firstly the color of Zn2SiO4:Mn lies closer to the 550 nm point on the spectral curve and therefore initially appears to be the obvious choice. On the other hand, it has been shown, according to the invention, that the production of Zn2SiO4:Mn is very problematic and, in particular under VUV irradiation, tends to instability, and in addition BaMgAl10O17:Mn, above all under the excitation preferred by the invention, shows a better quantum yield as a result of an Xe excimer discharge.
In the case of the remaining pair LaPO4:Ce,Tb and Y3Al5O12:Ce, it has been shown that LaPO4:Ce,Tb exhibits a considerably better yield under VUV excitation than Y3Al5O12:Ce and is therefore to be preferred.
In principle, however, it is also possible to manage with only two phosphors in the green area, which, in the case of the combination of BaMgAl10O17:Mn and BaMgAl10O17:Eu, is reduced to dual activation of the same host lattice, that is to say the phosphor BaMgAl10O17:Mn,Eu. The correct green color can then be set by the relative concentration of the activation elements Eu and Mn.
In the case of yellow signal colors, it is necessary to work relatively close to the spectral curve, where the relevant Standards are located. For this purpose, according to the invention, a mixture of (Y,Gd)BO3:Eu on the one hand and Zn2SiO4:Mn and/or LaPO4:Ce,Tb on the other hand is provided. In this case, LaPO4:Ce,Tb has a better yield than Zn2SiO4:Mn under VUV excitation, for which reason the combination (Y,Gd)BO3:Eu and LaPO4:Ce,Tb is preferred. As a result, the area of interest in the vicinity of the spectral curve can be reached, but it must not be overlooked that Zn2SiO4:Mn has an advantage over LaPO4:Ce,Tb as a result of its closer position to the spectral curve. If, therefore, a color locus particularly close to the spectral curve is desired, it is not possible to dispense with Zn2SiO4:Mn.
Particular difficulties have arisen in the case of signal red. The phosphor (Y,Gd)BO3:Eu, with an orange-colored main emission has a color which is located at too short a wavelength. Other red phosphors, such as Y2O2S:Eu or YVO4:Eu are, from this point of view, located very much more favorably in the color diagram.
On the other hand, it has been shown, according to the invention, that considerable yield problems actually occur in the case of signal red, and (Y,Gd)BO3:Eu has the best yield by far among the red phosphors in the VUV range, specifically considerably more so in real lamps than in the powder sample. According to the invention, therefore, the not quite optimal location of (Y,Gd)BO3:Eu is tolerated in order to achieve a yield which is sufficient for the practical application. Depending on the red Standard to be achieved, an additional red filter is then used. This is because it has been shown that, in spite of the filter losses, the combination of (Y,Gd)BO3:Eu and additional color filtering is ultimately more efficient than the use of a different red phosphor having a poorer yield. In this case, the filter should be as sharp-edged as possible and, for example with regard to the German Standard for traffic-lights red, should have a cut-off at about 595 nm.
Preferred fields of application of a signaling lamp according to the invention are luminous traffic signs or traffic signals, specifically both in road traffic and in rail or marine traffic. In this context, the invention primarily relates to a traffic light, in particular to the phosphor mixtures explained above for the colors green, yellow and red. However, a further, important field of application is also in motor-vehicle lamps, for example red rear lights, brake lights or yellow turn (up) indicators.
The short formulae used above for the various phosphors should be understood as follows for this application, the narrower lower limits and (irrespective of the lower) the narrower upper limits being understood to be correspondingly preferred in each case:
In addition to the ideal compositions described, compositions are also included which fall outside the abovementioned concentration ranges but are adjacent thereto and have the same phase.